To analyze immune-related adverse events (ir-AEs) in patients treated with radiation and immune checkpoint blockade.

We retrospectively reviewed records from patients with metastatic non-small cell lung cancer, melanoma, or renal cell cancer who received at least 1 cycle of a CTLA-4 or PD-1 inhibitor and radiation. Immune-related adverse events, defined using Common Terminology Criteria for Adverse Events version 4.0, were tabulated in relation to treatment variables, and associations with sequencing and timing were assessed.

We identified 133 patients, of whom 28 received a CTLA-4 inhibitor alone, 88 received a PD-1 inhibitor alone, and 17 received both classes of inhibitors either sequentially (n=13) or concurrently (n=4). Fifty-six patients received radiation within 14 days of an immune checkpoint inhibitor. Forty-six patients experienced at least 1 ir-AE (34.6%). Patients receiving both CTLA-4 and PD-1 inhibitors experienced more any-grade ir-AEs as compared with either individually (71% vs 29%, P=.0008). Any-grade ir-AEs occurred in 39% of patients in whom radiation was administered within 14 days of immunotherapy, compared with 23% of other patients (P=.06) and more often in patients who received higher equivalent dose in 2-Gy fractions (EQD2) EQD2 (P=.01). However, most toxicities were mild. There were no associations between site irradiated and specific ir-AEs.

Our data suggest the combination of focal palliative radiation and CTLA-4 and/or PD-1 inhibitors is well tolerated, with manageable ir-AEs that did not seem to be associated with the particular site irradiated. Although conclusions are limited by the heterogeneity of patients and treatments, and future confirmatory studies are needed, this information can help guide clinical practice for patients receiving immune checkpoint therapy who require palliative radiation therapy.